A passenger compartment of a vehicle is typically heated and cooled by a heating, ventilating, and air conditioning (HVAC) system. The HVAC system directs a flow of air through a heat exchanger to heat or cool the air prior to flowing into the passenger compartment. In the heat exchanger, energy is transferred between the air and a coolant such as a water-glycol coolant, for example. The air is normally supplied from ambient air or a mixture of air re-circulated from the passenger compartment and ambient air. Energy for heating and cooling of the passenger compartment of the vehicle is typically supplied from a fuel fed engine such as an internal combustion engine, for example.
In a hybrid vehicle, both a fuel fed engine and an electric motor are used to power a drive system for the vehicle. Thus, at times the fuel fed engine may be operating, the electric motor may be operating, and both the fuel fed engine and the electric motor may be operating. Therefore, the HVAC system in the hybrid vehicle must be capable of heating and cooling air during each of these operating modes. Examples of such systems are shown and described in commonly owned U.S. patent application Ser. No. 11/101,871 filed Apr. 8, 2005, hereby incorporated herein by reference in its entirety, and U.S. patent application Ser. No. 11/184,447 filed Jul. 19, 2005, hereby incorporated herein by reference in its entirety. If the fuel fed engine must be operating in order to operate the HVAC system in the hybrid vehicle, an efficiency thereof is reduced.
It would be desirable to produce a heating, ventilating, and air conditioning system for a hybrid vehicle, wherein an efficiency of operation of the hybrid vehicle during operation of the HVAC system is maximized.